1. Field of the Invention
The present invention relates to a terminal, for an engaging type connector, having an engaging part and a solder-bonding part.
2. Description of the Related Art
Mentioned in JP-A 2006-77307 is a conducting material, for a connecting part, having high electrical reliability (low contact resistance) and a low frictional property, and suitable for forming a terminal for an engaging type connector. The technique disclosed in JP-A 2006-77307 uses a copper alloy strip having a surface roughness greater than that of ordinary copper alloy strips as a base material, forms a plated Ni layer, a plated Cu layer and a plated Sn layer in that order, forms a plated Cu layer and a plated Sn layer in that order, or forms only a plated Sn layer on the surface of the base material, processes the plated Sn layer by a reflowing process to form a Cu—Sn alloy layer by the plated Cu layer and the plated Sn layer, or by the copper alloy base material and the plated Sn layer, and exposes the Cu—Sn alloy layer partly through the plated Sn layer smoothed by the reflowing process. (Parts of the Cu—Sn alloy layer corresponding to projections in the roughened surface of the base material are exposed.) The conducting material mentioned in JP-A 2006-77307, for connecting parts, formed after the reflowing process has a coating including the Cu—Sn alloy layer and the Sn layer, or the Ni layer, the Cu—Sn alloy layer and the Sn layer formed in that order, and in some cases, a Cu layer remains between the surface of the base material and the Cu—Sn alloy layer, or between the Ni layer and the Cu—Sn alloy layer. It is specified that the areal exposure ratio, namely, the areal ratio of the exposed parts, of the Cu—Sn alloy layer is between 3% and 75%, the Cu—Sn alloy layer has a mean thickness between 0.1 and 3.0 μm and a Cu content between 20 and 70 atomic % and the Sn layer has a mean thickness between 0.2 and 5.0 μm. It is mentioned in JP-A 2006-77307 that it is desirable that the surface of the base material has an arithmetic mean roughness Ra of 0.15 μm or above with respect to one direction and an arithmetic mean roughness Ra of 4.0 μm or below with respect to all directions, and intervals of the exposed parts of the Cu—Sn alloy layer are between 0.01 and 0.5 mm.
A conducting material for connecting parts corresponding to a subordinate concept of JP-A 2006-77307, and a method of manufacturing the conducting material are disclosed in JP-A 2006-183068. The construction of the plated layer and the construction of the coating after the reflowing process of the conducting material disclosed in JP-A 2006-183068 are the same as those of the conducting material disclosed in JP-A 2006-77307.
It is specified in JP-A 2006-183068 that the areal ratio of exposed parts of the Cu—Sn alloy layer of the conducting material, for a connecting part, after the reflowing process is between 3% and 75%, the Cu—Sn alloy layer has a mean thickness between 0.2 and 3.0 μm and a Cu content between 20 and 70 atomic % and the Sn layer has a mean thickness between 0.2 and 5.0 μm. It is mentioned in JP-A 2006-183068 that it is desirable that the surface of the base material has at least an arithmetic mean roughness Ra of 0.15 μm or above with respect to one direction and an arithmetic mean roughness Ra of 3.0 μm or below with respect to all directions. It is also mentioned that it is desirable that the surface of the base material has at least an arithmetic mean roughness Ra of 0.3 μm or above and an arithmetic mean roughness of 4.0 μm or below with respect to all directions, and intervals of the exposed parts of the Cu—Sn alloy layer at least in one direction are between 0.01 and 0.5 mm.
Techniques disclosed in JP-A 2004-300524, JP-A 2005-105307, and JP-A 2006-183298 process a Cu alloy strip by a punching process and Sn-plates the punched Cu alloy strip to coat the entire surface of the punched Cu alloy strip including edges of punched openings to provide terminals or the like having an improved solder-bonding property as compared with that of terminals made from a Cu alloy strip that is Sn-plated before being subjected to a punching process.
It is mentioned in JP-A 2004-68026 that a conducting material, for a connecting part, including a Cu alloy base material, and coating including a Ni layer, a Cu—Sn alloy layer, and a Sn layer is excellent in forming an engaging type terminal having a low frictional property when the Sn layer has a comparatively small thickness of 0.5 μm or below, and is excellent in solder-bonding property when the Sn layer has a comparatively big thickness greater than 0.5 μm.
Each of conducting materials, for a connecting part, disclosed in JP-A 2006-77307 and JP-A 2006-183068 includes a Sn layer forming an outermost layer, and a base material having a surface having a large surface roughness, and hence parts of the hard Cu—Sn alloy layer are exposed. Particularly, the Cu—Sn layer of the conducting material mentioned in JP-A 2006-183068 protrudes. Therefore, a terminal has high electrical reliability and a low frictional property and is suitable for use as an engaging type terminal. Since parts of the Cu—Sn alloy layer are exposed in the surface of the material, the material is inferior in solder-bonding property to a material entirely coated with a Sn layer.
An engaging type terminal having a soldering part, such as a pin terminal employed in a printed wiring board, is required to have a low frictional property so that the engaging type terminal can be fitted in a receiving part by a low pressure, and the soldering part is required to be excelling in solder-bonding property.
It is desirable to use either of the materials mentioned in JP-A 2006-77307 and JP-A 2006-183068 to form a terminal having a low frictional property. However those materials are unsatisfactory in solder-bonding property. Although the improvement of the solder-bonding property can be achieved by the postplating process as mentioned in those patent documents, it goes without saying that such an improvement is not a substantial improvement.
When a thick plated Sn layer is formed by a postplating process to improve the solder-bonding property as mentioned in JP-A 2004-68026, friction increases and hence the material is not suitable for forming an engaging type terminal.